1. Field of the Invention
The invention relates to a data recording and reproducing apparatus for recording and/or reproducing data and data editing method. More particularly, the invention relates to a data recording and reproducing apparatus and data editing method suitable for recording, reproducing and editing of video and audio data.
2. Description of the Related Art
In recent years, in accordance with multi-channeling for providing information due to the spread of a CATV (cable television) or the like, there has been a growing demand to simultaneously record, reproduce, or record and reproduce ha plurality of video and audio data with one video and audio data recording and reproducing apparatus, as distinct from a conventional VCR (Video Cassette Recorder). In response to this demand, an apparatus called a video server (also called an AV (Audio and/or Video) server) for recording and reproducing video and audio data by using a random-accessible recording medium such as a hard disk is coming into a widespread use.
Generally, video servers in broadcast stations require a high transfer rate of data and a large capacity for recording data over a long period of time, because of the demands on image quality and sound quality. Attempts have been therefore made to increase data transfer rate and capacity by using a data recording and reproducing apparatus including a plurality of hard disk (hereinafter referred to as HD) drives capable of storing the video and audio data and of performing parallel processing. Further attempts have been made to ensure reliability by previously recording parity data in case of trouble in any of the HD drives. It is thus possible to realize a multi-channel video server having various applications: for example, even when the number of channels required varies depending on the contents and broadcast form of a program which a broadcast station intends to provide, material data composed of a plurality of audio and video data is previously recorded separately and then multi-channel transmission is performed simultaneously, or the same material data is reproduced on multi-channel by shifting a reproducing time, whereby a system such as a VOD (Video On Demand) or an NVOD (Near Video On Demand) is established.
A data recording and reproducing apparatus for such a video server utilizes the technology of RAID (Redundant Arrays of Inexpensive Disks) comprising a plurality of hard disk drives (hereinafter referred to as HDDs), each HDD including a plurality of HDs, which is proposed in an article by Patterson et al., published in 1988 (“A Case for Redundant Arrays of Inexpensive Disks (RAID)”, ACM SIGMOND Conference, Chicago, Ill., Jun. 1-3, 1988).
In this article, the RAID is classified into five types, RAID-1 to RAID-5. The RAID-1 is a type of RAID which writes the same content onto two HDDs. The RAID-3 is a type of RAID which divides input data into the data having a fixed length and records the data on a plurality of HDDs while generating parity data that is exclusive OR of corresponding data blocks in the HDDs and writing the parity data onto another HDD. The RAID-5 is a type of RAID which divides data into a larger unit (block) and records one divided data on one HDD in the form of the data block while recording a result (parity data) of exclusive OR of corresponding data blocks in the HDDs on other HDDs in the form of a parity block and distributing the parity block to other HDDs.
For other RAIDs, refer to the above-described article.
On the other hand, materials for actual use in a news program, a sports program and so on are subjected to processing such as editing in a broadcast station, and then processed materials are transmitted. Particularly for the transmission of urgent materials for news programs, materials for sports programs in cases of an extension of a game time, or the like, reduction in an editing time is desired.
In a typical editing processing, an editing machine is connected to VCRs. Materials to be transmitted are selected while materials reproduced by a VCR for reproducing are checked by the editing machine. Selected materials are recorded by a VCR for recording, and then a recorded tape is transmitted from a VCR for transmission.
In an attempt to reduce an editing time, nonlinear editing is also performed nowadays. For example, an AV server described above is connected to an editing machine. Materials stored in the AV server are reproduced and materials to be transmitted are selected in the editing machine. Then materials to be transmitted stored in the AV server are transmitted in accordance with edit point information (also called EDL: Edit Decision List). Nonlinear editing, as distinct from linear editing by a conventional VCR or the like, enables an immediate search for a desired material and enhances free access to and reproduction of a desired material even if materials stored in the AV server are not in chronological order.
However, nonlinear editing also has a problem that an editing machine, aside from an AV server, has to be provided in a broadcast station and thus additional space for an editing machine is required. This is a serious problem for, particularly, a relay car having a limited space. Also, in order to give special effects on materials to be transmitted, it is necessary to further install a special effect apparatus separately.
Moreover, few editors are, in fact, accustomed to the operation of the above-described nonlinear editing. Even in actual broadcast stations, linear editing using tapes as a medium has been heretofore performed and many editors are accustomed to linear editing.
Furthermore, nonlinear editing by using an AV server and an editing machine has another problem: for example, even simple cutting can not be done instantaneously due to time division control of storage media of an AV server. An AV server comprises a plurality of channels (a plurality of I/Os). Each channel makes time division access to HDDs in order to arbitrate use of the HDDs that are recording media, or in order to arbitrate use of internal buses connected to the HDDs. This time division control results in a certain amount of loss of time until materials are transmitted in response to a command from the editing machine. The loss of time is considered as one cause of inconvenience of operation for editors.